1. Field of the Invention
The present invention relates to an indicating-needle type meter device, and in particular to magnetic excitation control of the indicating-needle type meter device that drives an indicating-needle using a stepping motor and a gear mechanism.
2. Description of the Related Art
Japanese Patent No. 4176984 discloses an indicating-needle type meter device that drives an indicating-needle using a stepping motor and a gear mechanism. In the indicating-needle type meter device disclosed in Japanese Patent No. 4176984, a drive shaft of the stepping motor is coupled to a rotating shaft of the indicating-needle via the gear mechanism. When the stepping motor is driven, gears of the gear mechanism are rotated, the rotating shaft of the indicating-needle is rotated, and the direction indicated by the indicating-needle is thus changed. Graduations on a dial plate are arranged at the positions indicated by the tip of the indicating-needle. By appropriately controlling the rotational position of the indicating-needle, instruments including speed meters and tachometers can indicate a measured value with the indicating-needle.
To drive the indicating-needle using the stepping motor, the indicating-needle type meter device sequentially switches an electric current flowing through a plurality of exciting coils housed in the stepping motor, thereby controlling the driving amount in a stepping manner. By controlling an excitation signal to grasp the stepping number in the driving, it is possible to manage the rotational position of the indicating-needle.
Because of some causes, such as vibration of a vehicle and overlap of noise with input data, step-out may possibly temporarily occur in which the input signal to the stepping motor and the actual driving amount do not coincide with each other. If the step-out repeatedly occurs, the control system fails to accurately grasp the actual driving amount. To address this, the indicating-needle type meter device disclosed in Japanese Patent No. 4176984 includes a stopper arranged at a position where a part of the drive system or the indicating-needle (which is hereinafter referred to as an abutting portion, such as a pin-like member) can abut on the stopper. In initialization, such as in application of power, the indicating-needle type meter device rotates the indicating-needle to the position at which the abutting portion abuts on the stopper, thereby grasping the actual position of the indicating-needle with reference to the position.
In transmission of the driving force of the stepping motor to the indicating-needle using the gear mechanism, a difference arises between the driving amount of the control side and the moving amount of the indicating-needle because of an effect of a backlash (gap) present at a position where adjacent gears engage with each other in the gear mechanism. Specifically, in switching of the driving direction, the effect of the backlash temporality prevents the driving force from being transmitted to a control target, thereby causing hysteresis characteristics to appear. To address this, the device disclosed in Japanese Patent No. 4176984 controls the position of the indicating-needle while considering the effect of the backlash.
To prevent positional deviation caused by the effect of the backlash, the indicating-needle type meter device disclosed in Japanese Patent No. 4176984 performs origin return processing in the start of excitation, such as in the application of power. In the origin return processing, the indicating-needle type meter device determines the stopper position at which the abutting portion abuts on the stopper to be an excitation start position for an excitation signal. The indicating-needle type meter device returns the phase of the excitation signal by a predetermined reversal angle from the excitation start position. The indicating-needle type meter device then forwardly rotates the indicating-needle from the state where the abutting portion abuts on the stopper and the gear mechanism is put to one side to a position where the effect of the backlash is eliminated. By using the position as the origin position, the indicating-needle type meter device controls the position of the indicating-needle. The origin position is usually set to a position at which the indicating-needle indicates a 0 graduation position. The reversal angle is set to a value equal to or larger than an angle corresponding to a control period of the excitation signal required to eliminate the hysteresis characteristics.
With the origin return processing, the indicating-needle is reliably positioned at the origin position apart from the stopper position by the predetermined angle in the start of excitation. After the origin return processing is executed, normal control is performed on the position of the indicating-needle. In the normal control on the position of the indicating-needle, the indicating-needle type meter device performs control on the position of the indicating-needle while considering the backlash amount, thereby accurately positioning the indicating-needle at a target position.
To terminate the excitation after performing the normal indication control with the indicating-needle, the indicating-needle type meter device returns the phase of the excitation signal such that the indicating-needle is rotated in a backward direction to be positioned at the origin position, and then stops the excitation to the stepping motor. With the termination processing, the indicating-needle is positioned and stopped at the origin position with the abutting portion abutting on the stopper and with the gear mechanism put to one side. As a result, the indicating-needle is positioned at the origin position before the start of next excitation.
As described above, in the method for controlling the indicating-needle described in Japanese Patent No. 4176984, the indicating-needle is positioned at the origin position before the start of excitation. When resuming the excitation, the indicating-needle type meter device starts excitation control by setting the phase of the excitation signal at the excitation start position (control origin) and positioning the indicating-needle at the stopper position. As a result, the indicating-needle drastically moves from the origin position to the stopper position in the start of excitation. Such behavior of the indicating-needle may possibly be recognized as an unnatural movement by a driver who is viewing it.
To attach such an indicating-needle type meter device, it is necessary to place the indicating-needle into a predetermined position of a rotating shaft and press-fit and fix it. Recently, indicating-needle caps having special shapes have been employed, making positional deviation more likely to occur in the placing. To address such positional deviation of the indicating-needle, adjustment control is performed after the press-fitting of the indicating-needle as disclosed in Japanese Patent No. 4176984. It is thus possible to correct the position of the indicating-needle so as to prevent positional deviation with respect to the scale position. Specifically, the indicating-needle is originally driven such that the stopper position is apart from the origin position by a backlash angle corresponding to the backlash amount. By contrast, the technology disclosed in Japanese Patent No. 4176984 drives the indicating-needle such that the stopper position is apart from the origin position by an angle larger than the backlash angle. After the placing of the indicating-needle, the difference between the angles is measured to perform positional control on the indicating-needle using the measured value as a placing error. If indication adjustment is performed to correct the placing error, the stopper position is further apart from the origin position compared with a case where no indication adjustment is performed. As a result, the amount of drastic movement of the indicating-needle is further increased in the start of excitation.
One meter unit frequently includes a plurality of instruments, such as a speed meter and a tachometer. If the correction of the placing error described above is performed on each of the instruments, the behaviors of the respective indicating-needles may possibly differ from one another in the start of excitation because the placing error amounts are different between the instruments. Also with this difference, the behaviors of the indicating-needles are more likely to be recognized as unnatural movements. In addition, the correction of the placing error may possibly not be performed on some of the instruments.
If the correction amount of the placing error is larger than the amount corresponding to a half period of the excitation signal, the indicating-needle initially moves from the origin position not in the backward direction corresponding to the stopper direction but in the forward direction and then moves in the stopper direction, that is, jumping occurs. To prevent the jumping, it is conventionally necessary to make the correction amount of the placing error smaller than the amount corresponding to a half period of the excitation signal.
Because of these circumstances, there have recently been demands for the indicating-needle type meter devices that can prevent an unnatural behavior of the indicating-needle in the start of excitation.
As described above, the technology disclosed in Japanese Patent No. 4176984 places the indicating-needle such that the stopper position is apart from the origin position by an angle larger than the backlash angle corresponding to a predetermined separation amount. After the placing of the indicating-needle, the difference between the angles is measured to perform positional control on the indicating-needle using the measured value as a placing error. The method described in Japanese Patent No. 4176984, however, can permit a placing error in a direction in which the stopper position is away from the origin position but cannot permit a placing error in a direction in which the stopper position is closer to the origin position. Therefore, an operator (manufacturing apparatus) that performs the placing operation of the indicating-needle needs to place the indicating-needle into a position on the side in a specific direction with respect to the predetermined position. Consequently, there have recently been demands for the indicating-needle type meter devices that can increase the degree of freedom in correction of the placing error.